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Two-way coupled direct numerical simulations are used to investigate theeffects of inertial particles on self-sustained, turbulent coherent structures(i.e. the so-called the regeneration cycle) in plane Couette flow at lowReynolds number just above the onset of transition. Tests show two limitingbehaviors with increasing particle inertia, similar to the results from thelinear stability analysis of saffman, 1962: low-inertia particles trigger thelaminar-to-turbulent instability whereas high-inertia particles tend tostabilize turbulence due to the extra dissipation induced by particle-fluidcoupling. Furthermore, it is found that the streamwise coupling between phasesis the dominant factor in damping the turbulence and is highly related to thespatial distribution of the particles. The presence of particles in differentturbulent coherent structures (large scale vortices or large scale streaks)determines the turbulent kinetic energy of particulate phase, which is relatedto the particle response time scaled by the turnover time of large scalevortices. By quantitatively investigating the periodic character of the wholeregeneration cycle and the phase difference between linked sub-steps, we showthat the presence of inertial particles does not alter the periodic nature ofthe cycle or the relative length of each of the sub-steps. Instead,high-inertia particles greatly weaken the large-scale vortices as well as thestreamwise vorticity stretching and lift-up effects, thereby suppressing thefluctuating amplitude of the large scale streaks. The primary influence oflow-inertia particles, however, is to strengthen the large scale vortices,which fosters the cycle and ultimately reduces the critical Reynolds number.

Modulation of the turbulence regeneration cycle by inertial particles in planar Couette flow